i 

@OREST RESEARCH NOTE

NORTHEASTERN FOREST EXPERIMENT STATION ' 

Upper Darby , Pennsylvania 

No. 48 

1955 

C 

A Dual-Bozzle System ?f 7 

Por IBs t Blowers 

One of the most serious problems in spraying tree@$-60 

control insects and diseases has been to obtafn a sufficient ' 

deposit in the upper parts of tall trees. 

A wide spray stream of fine droplets (35 to 45 microns in diameter) is ideal for treating the lower parts of - 

thetree. However, bythetimetheairstreamreaches the 

e tops of talltrees, its speed has so diminished that not. 

enough of the small droplets hit and stick. Larger drops 

(60 to 80 microns in diameter) are needed to get the spray 

deposited on the upper t'ree bark and foliage. 

This problem has been at least partly remedied by 

using a duel-nozzle system (fig. 1). With this, the lower 

portion of the tree near the mist blower can be treated with 

a fine spray, which gets maximum coverage yet does a minimum 

of damage to the foliage; and the upper portion of the tree 

cmn can be treated with a coarser spray. 

I 

Figure 1 6 

A dual-nozzle spray 

system. The coarse 

solid-stream nozzle 

is in the center. 

Notice the ring of 

4 fine-spray atomizing n~z.zles set 

at right angles to 

, a the air blast. Two 

separate shut-off 

valves are used. 

I 1 

1, 
Use of a coarse-spray nozzle is limited by the range 

in air velocity and volume. This determines the orifice 

size, pressure, and type of nozzle to install. If velocity 

and volume are too low, the large drops will fall. out of the 

air stream too quickly. On the' other hand, if the velocity 

is above 125 m.p.h., provision must be made for preventing 

too fine atomization by the shearing action of the air 

stream. 

For Uhe high-velocity rigs, it is necessary to use a 

coarsely atomizing nozzle. This can be either a cone type 

such as wwrljet No. 5 or No. 10, or a solid-stream nozzle 

with three 1 '16-inch orifices, such as the one shown in figure 1. Spray streams from the orifices should leave the nozzle at an a le of about 35 degrees from the line of the air 

blast. If t ? e angle is top great the spray may break out of 

the air stream. 

The coarse nozzle should be located in the center of 

the outlet and pointed with the air blast. The pump pressure 

should be kept under 60 pounds. The output of this nozzle 

should be about the same as the combined output of the ring 

of finely atomizing nozzles. 

The two sets of nozzles are not used at the sametime. 

Therefore, to spray with one set of'nozzles at a time, two 

shut-off valves are used, one for each system. The operator 

simply uses one quick-acting off-and-on valve to turn the 

spray on and off for the ring of fine nozzles, and another 

similar valve to turn the coarse spray nozzle on andoff. A 

more simple method for operating the two noz2le systems 

would be to install a three-way valve that can be operated 

with a single lever. Several valve and sprayer compa~es 

have this type of valve in stock. 

Machines that deliver 95 to 110 m.p.h. air velocity 

at 17,000 to 24,000 c.f.m. of air are well suited for carrying the large droplets to the tops of tall trees. With this 

a system it has been possible to practically double the quantity of chemical deposited at the top of tall trees. This 

has been determined from samples taken at 5-foot intervals 

from the ground to the top of a 70-foot elm tree. 

-43. F. POTTS 

Forest Insect and Disease Laboratory 

Northeastern Forest Experiment Station 

Forest Service, U.S . Dept . Agriculture 

New Haven, Connecticut 

2 Agriculture-Forest Service-Upper Darby, Pa. 

F